Bacterial Spores Bacteria are very resistant to all environments. A protective coating on the surface helps the bacteria evade  the  defense  mechanisms  of  the  body  and generally makes it more durable. Not all bacteria will take on the form of a spore’s shell-like coating to withstand unfavorable conditions. Bacteria in a spore state remain alive but passive, and they are resistant to the effects of heat, drying, and most bactericidal chemicals. They will remain capable of becoming virulent (strongly pathogenic) again under   favorable   conditions. However,  under unfavorable conditions, they will either die or remain dormant in a spore state until another opportunity for growth presents itself. Viruses Viruses   are   micro-organisms   that   are   much smaller than bacteria. Viruses vary in size, from being the size of a single protein molecule to the size of a more complicated bacterial cell. They can be so small that  they  can  be  seen  only  through  an  electron microscope. Viruses cannot live long or reproduce outside of a living body (host). They must be able to enter and live in specific cells. For descriptive purposes, they are customarily  divided  into  three  subgroups,  based  on host specificity: 1. Bacterial viruses 2. Animal viruses (including those that attack humans) 3. Plant viruses Some of the most common diseases caused by viruses are colds, smallpox, measles, rubella, herpes simplex,   AIDS,   infectious   hepatitis,   and   serum hepatitis. Viruses  are  usually  not  affected  by therapeutic  treatment  with  antibiotics.  Generally, therapeutic treatment is not used to combat a viral infection,  but  used  to  treat  a  secondary  bacterial infection that may develop. Most  viruses  are  susceptible  to  immersion  in boiling water for at least 20 minutes. There are two major exceptions to this rule, infectious hepatitis and serum hepatitis. Because of these exceptions to heat resistance, autoclaving for a minimum of 20 minutes at 270°F, or dry heat sterilization for 90 minutes at 320°F are the only safe procedures for control of these two viruses. 9-2 PROTOZOA Protozoa are single-celled animals that do not have a  rigid  cell  wall. Some protozoa cause parasitic diseases but not all are pathogens. Most species are harmless, living on dead organic matter or bacteria. Protozoa that are pathogenic survive freely in nature and must be spread by a carrier. Most protozoa pass through a life-cycle, meaning that they have definite stages of development. These stages vary for each species and are usually very complicated. Malaria is an example of a disease that is caused by protozoa. FUNGI Fungi,  like  bacteria,  are  plants  that  lack chlorophyll.  They  are  free-living  organisms  that  are smaller than protozoa. Mold and yeast forms of fungi have firm cell walls and resemble plants more than animals. Molds usually form cells in long chains or threads that grow into tangled masses. Some threads of the mass bear clusters of seedlike spores that, when dry, are  easily  blown  into  the  air  like  dust.  Each microscopic seed is capable of growing new mold upon settling in a suitable place. Mold spores are easily destroyed by heat. The most common infections in humans because of mold are athlete’s foot and ringworm.   The mold penicillium is very common in nature and contributes to the spoilage of food. The drug penicillium is derived from this mold. INFECTION CONTROL TERMS AND DEFINITIONS The following terms and their definitions will help you understand the material that is in this chapter and  in  chapter  10,  “Sterilization  and  Disinfection,” Volume 1: Asepsis—The prevention of contact with micro- organisms. Automated   washer   processor—Washer, sterilizer,  dishwasher,  or  other  mechanical  washing device. Barrier  technique—The use of rubber, plastic, foil, or other fluid resistant materials to cover surfaces and protect them from contamination. Bioburden —The  number  of  micro-organisms contaminating  an  object.  Also  known  as  bioload  or microbial load.